The present invention relates to A method of coupling active semiconductor components and also to such a coupling and then particularly to a series-connection of such couplings that will enable high voltages to be controlled.
Hitherto, a large number of components have been required in order, to control high voltages by connecting together semiconductor components in series, wherewith a pair of additional transistors resistances andxe2x80x94diodes are normally required in addition to the xe2x80x9cactuallyxe2x80x9d active transistor, which makes the couplings expensive. An example of one such known coupling is illustrated in FIG. 1, which shows a series-connection of two MOS-based power transistors that are coupled to control a voltage of some kV. This earlier known coupling is illustrated and described in the book xe2x80x9cPOWER MOSFETS Theory and Applicationsxe2x80x9d by Duncan A. Grant and John Gowar, published by John Wiley. and Sons. In a known application, it has previously only been found practical to apply across a transistor a voltage of at most 2000 V. It will be apparent that in order to be able to control still higher voltages while Using the same principles, the coupling will become even more extensive and comprehensive with further components needing to be connected in series.
In the power distribution field for instance, it is necessary to be able to control voltages of up to 100,000 V or still higher, while voltages of up to about 25,000 V are handled in respect of railroad and trolley car traffic for instance.
Accordingly, an object of the present invention is to provide a method which will enable active semiconductor components to be connected in series without complicated and expensive peripheral coupling so as to enable high voltages to be controlled at low cost.
These objects are achieved in accordance with the invention by taking a voltage from semiconductor component and applying this voltage to the control input of the next following semiconductor component and locking said voltage at a predetermined highest level.
According to one preferred embodiment of the invention, the semiconductor component is a transistor that includes floating metal-contacted protective rings and said voltage is taken from one of these protective rings.
A typical method, of terminating a high voltage semiconductor component is to use the aforesaid floating metal-contacted protective rings. The principle construction of the outer part of such a transistor is shown in FIG. 2, which also shows the depletion area of a transistor in the form of a curve and the active part is shown on the left. When the voltage across the active part of the transistor increases, the depletion area will reach the first protective ring at a voltage V1, and this ring will then adopt the voltage V1. At the voltage V2, the depletion area will have reached the second protective ring, which then adopts the voltage V2, and so on. One of the last protective rings has the potential Vf, this potential being utilised in the invention as described hereinafter in more detail.